patches: patch DateTime 2.12.7 to prevent DateTime.DateTime._dt_reconstructor in pickle

Having DateTime.DateTime._dt_reconstructor in pickles is not really
a problem, because DateTime keep compatibility for this, but it makes
Business Template output different between DateTime 2 and DateTime 3.

product/ERP5Type/patches/DateTimePatch.py

@@ -28,6 +28,7 @@
 
 from DateTime import DateTime as DateTimeKlass
 import math
+import six
 from DateTime.DateTime import _calcSD, _calcDependentSecond, _calcYMDHMS,\
 getDefaultDateFormat, _correctYear, _calcHMS, _calcDependentSecond2, DateTimeError,\
 SyntaxError, DateError, TimeError, localtime, time
@@ -248,6 +249,45 @@ def DateTime_parse(self, st, datefmt=getDefaultDateFormat()):
 
 DateTimeKlass._parse = DateTime_parse
 
+
+# DateTime 2.12.7 and 2.12.8 shipped with a monkey patch to copy_reg module,
+# introduced in zopefoundation/DateTime commit 1bb6e68 (Added forward
+# compatibility with DateTime 3 pickle format., 2012-08-10).
+# This patch was problematic, because copy_reg._reconstructor is included in
+# pickle protocol 1, (which is the protocol used by business template):
+#
+# >>> import pickle
+# >>> class C(object):
+# ...   pass
+# ...
+# >>> pickle.dumps(C(), 1)
+# 'ccopy_reg\n_reconstructor\nq\x00(c__main__\nC\nq\x01c__builtin__\nobject\nq\x02Ntq\x03Rq\x04.'
+#
+# because copyreg._reconstructor was monkey patched to be
+# DateTime.DateTime._dt_reconstructor, the pickles included reference to
+# DateTime.DateTime._dt_reconstructor.
+# After DateTime monkey patch was loaded, the pickle was like this:
+#
+# >>> pickle.dumps(C(), 1)
+# 'cDateTime.DateTime\n_dt_reconstructor\nq\x00(c__main__\nC\nq\x01c__builtin__\nobject\nq\x02Ntq\x03Rq\x04.'
+#
+# To prevent this to appear in pickle, we monkey patch the monkey patched
+# functions, to restore the original copy_reg._reconstructor name.
+#
+# Note that DateTime 3 provides support for this, it has DateTime.DateTime._dt_reconstructor
+# symbol, but that is no longer monkey patched in copy_reg, it is only here
+# for compatibility, because the symbol appears in pickle. For reference,
+# this was fe81af1 (Add `_dt_reconstructor` function introduced in DateTime
+# 2.12.7., 2012-09-17)
+if six.PY2:
+  # only apply the patch on python 2, because on python3 we have DateTime > 3
+  # and because copy_reg was renamed on python3
+  import copy_reg
+  if copy_reg._reconstructor.__module__ != 'copy_reg':
+    copy_reg._reconstructor.__module__ = 'copy_reg'
+    copy_reg._reconstructor.__name__ = '_reconstructor'
+
+
 if __name__ == '__main__':
   for i in ('2007/01/02 12:34:56.789',
             '2007/01/02 12:34:56.789 GMT+0200',